Dose monitoring and adjustment: aPTT tests will be measured at baseline and at regular intervals thereafter. Adjustment of the heparin dose will be made using a heparin nomogram (see below) if the aPTT is not at the target level of greater than 35 seconds and less than 50 seconds. aPTT levels will be monitored every six hours routinely. If a significant change is made to the heparin infusion rate due to a prolonged aPTT, the aPTT will be checked at a shorter interval of three hours to ensure that aPTT is not persistently at a supratherapeutic level as this could increase risk for bleeding complications.